1. Field of the Invention
The present invention relates generally to Multimedia Broadcast/Multicast Service (MBMS). In particular, the present invention relates to a method for controlling the selection of a frequency layer on which a connected mode User Equipment (UE) is to receive an MBMS service.
2. Description of the Related Art
The development of communication technology has lead to a Wideband Code Division Multiple Access (WCDMA) scheme that provides multimedia broadcasting/telecommunications services involving the transmission of a large volume of packet data or multimedia data, beyond the traditional voice service. In this context, the use of MBMS which services multiple UEs from one or more multimedia data sources is under discussion to support the multimedia broadcasting/telecommunications.
The MBMS is a service designed to transmit the same multimedia data to a plurality of recipients over a wireless network. As the recipients share one radio channel, radio resources can be conserved. The MBMS supports Frequency Layer Convergence (FLC) with the aim of more efficient use of radio resources. The FLC is the process of transmitting an MBMS service at only one specified frequency rather than providing the MBMS service at all overlapped frequencies available within the same area, and requesting UEs that want to receive the MBMS service to preferentially re-select the specified frequency. This specified frequency is called the preferred frequency or preferred frequency layer (PL) of the MBMS service. The UEs perform an MBMS frequency selection procedure according to the FLC.
When an MBMS session starts for an MBMS service, the PL for the MBMS service is decided by Radio Resource Management (RRM). Because an idle mode UE does not have associated traffic, even though it has joined the MBMS service from a different frequency layer and reselects to the PL, this does not affect the state of the system resources. In contrast, a connected mode UE receiving a dedicated traffic service has associated traffic and thus it may not receive the dedicated service on the PL depending on the radio resource availability of the PL. If the radio resources of the PL are not sufficient to accommodate the traffic of the connected mode UE, the dedicated service is not available any longer.